A Fresnel lens sheet 70 shown in FIG. 7 is disclosed in, for example, JP60-173533A and JP61-208041A. As shown in FIG. 7, the Fresnel lens sheet 70 has a light-receiving surface 71 provided with a prism set 72 including a plurality of parallel prisms 73. Each prism 73 has a totally reflecting surface 74 to reflect incoming light totally toward a viewing side.
The Fresnel lens sheet having such construction permits a light source disposed behind the light-receiving surface of the Fresnel lens 70 to project light (images) at an acute angle to the Fresnel lens sheet 70, which enables the forming of a thin projection television receiver.
However, some incident light rays fallen on the rear surface of the Fresnel lens sheet do not fall on the totally reflecting surfaces 74 and are totally reflected by the front surface, i.e., light-emitting surface. Such light rays that are totally reflected by the front surface will be referred to, in some cases, as stray light rays in the following description. If stray light rays are produced, an image looks double, i.e., a double image is displayed or a ghost image appears, and the contrast of the image decreases.
As shown in FIG. 8, when light rays 80 fall on the light-receiving surface 71 of the Fresnel lens sheet 70, the Fresnel lens sheet 70 emits both ideal light rays 80A, and undesired light rays 80B that form a ghost image from the light-emitting surface 75.
In JP62-113131A, an invention for solving the problem resulting from the stray light rays diffuses light rays that do not fall on the totally reflecting surfaces of prisms, namely, stray light rays, to make the ghost image ambiguous.
Although this previously proposed invention is able to make the ghost image formed by the stray light rays ambiguous and faint, the contrast of the image decreases unavoidably because there still exist the diffused stray light rays.
Inventions disclosed in, for example, JP63-139331A, JP63-30835A, JP63-32528A and JP5-72634A, form light-absorbing layers in parts, through which totally reflected light rays (images) do not travel, of a Fresnel lens sheet to absorb stray light rays.
Those previously proposed inventions, however, need to adjust the positional relation between the prism and the light-absorbing layers so that the prisms and the light-receiving layers match precisely with each other. If the prisms and the light-absorbing layers are not formed in correct positional relation, it is possible that light rays (images) that must reach the viewer are absorbed. Thus, it is practically very difficult to manufacture Fresnel lens sheets of those previously disclosed inventions. Moreover, even among those previously disclosed inventions, some produce stray light rays and hence effective light rays are reduced accordingly.